Seal swelling agents, such as esters, adipates, sebacates, azeealates, phthalates, sulfones, alcohols, alkylbenzenes, substituted sulfolanes, aromatics, or mineral oils, are introduced into functional fluids used in machinery in order to minimize seal shrinkage. Examples of functional fluids include automatic transmission fluids, hydraulic fluids, lubricants, and other fluids used in heat exchange equipment. Seal swelling agents are used to address the problem of seal shrinkage, wherein seals shrink and ultimately cause functional fluid leakage. When the functional fluid is lost, machinery can slowly breakdown or stop working altogether.
A number of seal swelling agents are known in the art including those listed above. One seal swelling agent of particular interest is a substituted sulfolane as described for example in U.S. Pat. No. 4,029,588 to Koch, the disclosure of which is incorporated herein by reference. However, substituted sulfolanes often include undesirable impurities. These impurities include water, catalyst, unreacted sulfolene, and/or unreacted alcohol. Water has a particularly adverse effect on elastomeric seals commonly used in lubricant applications.
Because of the impurity levels in substituted sulfolanes, and an inability to remove the impurities economically, many companies have chosen to use other seal swell agent additives. One such compound is a naphthalene depleted aromatic compound commercially available from Exxon Mobil Corporation under the trade name AROMATIC 200 ND (hereinafter, “200 ND”). However, the treat rate for 200 ND is relatively high and 200 ND emits an unpleasant odor. Therefore, there is a continuing need to find cost-effective ways to maximize the positive aspects of suitable seal swell agents while minimizing undesirable characteristics of the agents.